Hastelloy S

Designated as UNS N06635, Hastelloy S (also known as “Alloy S”), is a nickel-based high-temperature alloy with excellent thermal stability, low thermal expansion, and oxidation resistance to 1095°C[2000°F]. It retains strength and ductility after aging at temperature of 425 to 870°C[800 to 1600°F]. Hastelloy S is mainly developed for applications involving severely cyclical heating conditions where components must be capable of retaining strength, ductility, and metallurgical integrity after long time exposure and are extensively used as seal rings in gas turbine engines where its low thermal expansion coefficients is also important.

Hastelloy S ring gasket manufactured to ASME B16.20, Octagonal R24.

1. Chemical Composition Requirements

The Chemical Compostion of Hastelloy S, %

Ni

Balance

Cr

14.5-17.0

Fe

≤3.0

Co

≤2.0

Mo

14.0-16.5

W

≤1.0

Al

0.10-0.50

C

≤0.02

Mn

0.30-1.00

Si

0.2-0.75

B

≤0.015

La

0.01-0.10

Cu

≤0.35

2. Mechanical Properties of Hastelloy S

Tensile Strength, min.

Yield Strength, min

Elongation, min.

Hardness, min

Mpa

ksi

Mpa

ksi

%

HRA

835

121

445

64.5

49

52

3. Physical Properties of Hastelloy S

Density

Melting Range

Specific Heat

Electrical Resistivity

g/cm3

°C

°F

J/kg. k

Btu/lb.°F

µΩ·m

8.75

1335-1380

2435-2516

398

0.095

1280

4. Workability, Weldability & Heat Treatment of Hastelloy S

The UNS N06635(Hastelloy S) alloy can be readily forged and cold worked due to its excellent ductility. It can be welded by both manual and automatic welding methods including gas tungsten arc(GTAW), and gas metal arc(GMAW). Forging should be performed from 1146°C to 872°C up to the final 20% cross-section reduction. The final 20% reduction should be done from about 1039°C to 817°C. Hastelloy S alloy should be solution annealed at the temperature of 1065°C then followed by cooling in air or hydrogen. Cooling rates during heat treatment have no virtual effect on its mechanical properties due to its stable nature.

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